docs: def common_timeline(self, reference, hypothesis):
          """Return timeline common to both reference and hypothesis
  
          reference   |--------|    |------------|     |---------|         |----|
          hypothesis     |--------------| |------|   |----------------|
          timeline    |--|-----|----|---|-|------|   |-|---------|----|    |----|
  
          Parameters
          ----------
          reference : Annotation
          hypothesis : Annotation
  
          Returns
          -------
          timeline : Timeline
          """
          timeline = reference.get_timeline(copy=True)
          timeline.update(hypothesis.get_timeline(copy=False))
          return timeline.segmentation()